#include"Digamma.h"
double digamma(double x){
  double result = 0, xx, xx2, xx4;
  assert(x > 0);
  for ( ; x < 7; ++x)
    result -= 1/x;
  x -= 1.0/2.0;
  xx = 1.0/x;
  xx2 = xx*xx;
  xx4 = xx2*xx2;
  result += log(x)+(1./24.)*xx2-(7.0/960.0)*xx4+(31.0/8064.0)*xx4*xx2-(127.0/30720.0)*xx4*xx4;
  return result;
}
